The studies proposed here are designed to examine relationships between maternal metabolism and endocrine status on fetal growth and development. A key tissue involved in this interaction is the placenta. Since the placentas are of two sources (maternal and fetal), they may respond differently to variations in maternal serum (hormones, glucose, lipid, etc.). Because of the limited data available on both fetal and maternal placental changes during the critical third trimester of gestation, the experiments described in Series 1 are proposed. Our preliminary data show that placentas from both origins are actively converting glucose to fatty acids and that this rate of synthesis is higher than that of maternal liver. Because of the dynamic nature of the placenta during gestation, it is important: 1) to know at what stages the highest rates of lipogenesis and gluconeogenesis are attained, and 2) to compare these changes in activity with other tissues influenced by pregnancy (i.e., maternal liver and adipose). As pointed out in the background section, in the rat the metabolic state of the dam changes from anabolic to catabolic during the last trimester. This may lead to changes in the types of nutrients available to the fetus unless the placenta adapts and maintains a constant flow of either glucose or some other metabolite (fatty acid, ketone body, lactate). These adaptations may also precipitate diabetes (gestation) in latent diabetics. There is some indication that this occurs in the rat placenta toward the end of the term when the activities of placental gluconeogenic enzymes rise.